Reworked LV2 plug-ing support.

This enables all platforms to use LV2 plugins in non-GUI mode.  There is
still some work to do, like subgroup handling and better scalepoint
handling.

src/AudacityApp.cpp

@@ -161,6 +161,10 @@ It handles initialization and termination by subclassing wxApp.
 #     pragma comment(lib, "libvorbis")
 #  endif
 
+#  if defined(USE_LV2)
+#     pragma comment(lib, "lv2")
+#  endif
+
 #  if defined(USE_MIDI)
 #     pragma comment(lib, "portsmf")
 #     endif